A conventional cooling fan usually includes a fan frame, a bearing cup, a hub and a plurality of blades, a circuit board, and a stator assembly.
With the constantly widened applications in different fields thereof, the cooling fan has been used with many electronic devices with special purposes, such as central processing units (CPU), servers, power supplies, communication chassis, and telecommunication base stations. These electronic devices are also often used in very severe environments, such as humid, wet, and salt spray environments. Since general cooling fans, particularly the circuit board and bearing cup thereof, are not provided with any protective structure against water and salt spray, they are apparently not suitable for use in such severe environments. The circuit board and bearing cup inside the fan are subjected to corrosion by the salt spray accumulated thereon, and the corroded circuit board and bearing cup would lead to a stuck and immovable fan and shorten the service life of the fan.
To solve the above problem, a solution involving injection molding has been proposed. According to the injection molding solution, the stator assembly and the circuit board are first assembled to the fan frame to form a subassembly, and then, put the subassembly in a mold and inject a molding material into the mold. After the molding material is hardened, the subassembly is enclosed in the molding material and then removed from the mold. The molding material not only encloses the subassembly, but also fills up all internal spaces in between the stator assembly, the circuit board and the bearing cup, so as to provide the effect of water and salt spray resistance. However, since the molded injection material is thick, it would have adverse influence on the heat dissipation of the electronic components enclosed in the molding material to result in burned-out electronic components.
Further, the above-described injection molding solution is mainly used to protect the electronic components against short circuit and burnout due to corrosion caused by accumulated water and salt spray, and is not effective in terms of stopping the salt spray from accumulation. The main effect that can be achieved by the injection molding solution is water resistance. Further, the fan motor being enclosed in the injected molding material to protect the circuit board against water and salt spray has obviously reduced heat dissipation performance, which tends to result in an elevated temperature of the whole motor. Moreover, the salt spray accumulated in the fan motor enclosed in the injection molding material tends to form salt grains due to high temperature. The salt grains are attached to the interior of the fan to result in stuck fan and burned-out circuit board
In brief, the conventional water and salt spray resistant structures for cooling fan have the following disadvantages: (1) shortening the fan service life; (2) causing accumulated heat inside the fan; and (3) lowering the heat dissipation efficiency of the fan.